Differential L-shell radiative recombination rate coefficients for bare uranium ions interacting with low-energy electrons

Results of the calculations of differential L?shell radiative recombination (RR) rate coefficients for bare uranium ions colliding with free electrons using the nonrelativistic dipole approximation and fully relativistic calculations are reported. The rate coefficients were obtained for very low, in the range of meV, relative electron-ion energies. We demonstrate that even for such low relative ion-electron energies the relativistic effects significantly modify the differential RR rate coefficients for the L?subshells and, as a result, the measurements of the relative electron energy dependence of the L-RR rates could be used for studying of the relativistic effects. These effects are strongest for the L ₃-subshell, which is discussed here in more details.     

Exact inclusion of the Coulomb field in the photobeta decay of a nucleus and problem of bypassed elements

The probability of the endothermic β^? decay of nuclei that is stimulated by an electromagnetic field of Planck frequency spectrum (photobeta decay) is calculated, the effect of the Coulomb field on a relativistic electron and a virtual relativistic positron being exactly taken into account in this calculation. It is shown that the inclusion of Coulomb effects is of paramount importance and that the results of the calculations may differ by an order of magnitude from those that were obtained previously in the plane-wave approximation, depending on the energy range being considered. A model for the synthesis of bypassed elements in the interior of massive stars is proposed on the basis of the mechanism of the photobeta decay of stable elements that originate from s and r processes.     

Properties of doubly heavy baryons in the relativistic quark model

Mass spectra and semileptonic decay rates of baryons consisting of two heavy (b or c) and one light quark are calculated in the framework of the relativistic quark model. The doubly heavy baryons are treated in the quark-diquark approximation. The ground and excited states of both the diquark and quark-diquark bound systems are considered. The quark-diquark potential is constructed. The light quark is treated completely relativistically, while the expansion in the inverse heavy-quark mass is used. The weak transition amplitudes of heavy diquarks bb and bc going, respectively, to bc and cc are explicitly expressed through the overlap integrals of the diquark wave functions in the whole accessible kinematic range. The relativistic baryon wave functions of the quark-diquark bound system are used for the calculation of the decay matrix elements, the Isgur-Wise function, and decay rates in the heavy-quark limit.     

Energies, Auger and radiative probabilities of the doubly-excited 1s23l3l′ states for Be-like neon

Energy levels, Auger decay and radiative transition rates of the doubly-excited 1s ²3l3l′ states for Be-like neon are calculated using relativistic Multiconfiguration Dirac-Fock (MCDF) method. Electron correlation and relaxation effects are taken into account. The magnitude of Auger rates for the 35 doubly-excited states and their decay channels are discussed. Present calculated values are in agreement with the latest experimental electron spectra as well as other theoretical results.     

Effects of multiple QCD and QED radiations in semileptonic decays of top particles

The charged lepton spectrum in semileptonic decays of top particles is calculated including the effects of multiple QCD and QED radiations, treated in the leading logarithm approximation. A comparison with QCDO(α _S ) results is made. Nonperturbative effects associated with the hadronization of the decay partons are also discussed. The effects of QED radiation are found to be important. Calculations have been done by means of a Monte Carlo algorithm, which also allows to calculate the full decay final state.     

Distribution and polarization of λ produced from Β decays of polarized ξ;−

The distribution and the polarization of the final baryon are calculated for baryon\ decay and for the cascade decay:Ξ; ^{?→σ 0} v(σ ⁰→λγ. These calculations are made under the approximation of neglecting the electron mass and keeping only zeroth and first order terms in the energy release. It is discussed how the weak coupling constants in the cascade decay and in the simple decayΞ ^? →λv can be determined without detection of the emittedγ.     

Exact Path-Integral Representations for the T-Matrix in Nonrelativistic Potential Scattering

Several path integral representations for the T-matrix in nonrelativistic potential scattering are given which produce the complete Born series when expanded to all orders and the eikonal approximation if the quantum fluctuations are suppressed. They are obtained with the help of ??phantom?? degrees of freedom which take away explicit phases that diverge for asymptotic times. Energy conservation is enforced by imposing a Faddeev?CPopov-like constraint in the velocity path integral. An attempt is made to evaluate stochastically the real-time path integral for potential scattering and generalizations to relativistic scattering are discussed.     

Constraints on the decay rates of quarkonium

We derive inequalities between the leptonic decay rates of 1S and 2S states of quarkonium, when the binding potential is an increasing concave (convex) function of the inter-quark distance in a framework where some relativistic corrections have been made to the Van Royen-Weisskopf formula for these rates. Experimental decay rates of the γ and γ′ rule out the convex increasing potential.     

Resonance conversion as a dominant decay mode for the 3.5-eV isomer in 229m Th

on the basis of calculations performed withi nthe relativistic multiconfiguration Dirac-Fock method, it is shown that the probability of the decay of the 3.5-eV nuclear level in the ^229m Th isomer via resonance conversion exceeds the probability of its direct radiative decay by at least a factor of about 600. The possibility of experimentally observing delayed soft photons or alpha particles in the decay of this isomer is discussed.     

Relativistic corrections of the electromagnetic current in a one-pion exchange model

Photon absorption or emission in nucleon-nucleon collisions is studied in the one-pion exchange approximation. A gauge-invariant expansion in 1/m is obtained for the isoscalar electro-magnetic current. Kinematic and dynamic relativistic corrections are discussed.     

Relativistic theory of atom-laser interactions at very high laser intensities

The high-frequency approximation of Kristi? and Mittleman is considered in detail as a basis for the relativistic theory of atom-laser interactions. The properties of the 3D potentials are discussed. Within a one-dimensional model similar to that employed by Kylstra, Ermolaev, and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass-shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, the frequency ω and the peak field strength ?₀, the 1D bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of the field strengths where, in the zeroth order of the high-frequency approximation, the binding is stabilized by the field.     

New approach for alpha decay half-lives of superheavy nuclei and applicability of WKB approximation

The α decay half-lives of recently synthesized superheavy nuclei (SHN) are calculated by applying a new approach which estimates them with the help of their neighbors based on some simple formulas. The estimated half-life values are in very good agreement with the experimental ones, indicating the reliability of the experimental observations and measurements to a large extent as well as the predictive power of our approach. The second part of this work is to test the applicability of the Wentzel-Kramers-Brillouin (WKB) approximation for the quantum mechanical tunneling probability. We calculated the accurate barrier penetrability for alpha decay along with proton and cluster radioactivity by numerically solving Schrödinger equation. The calculated results are compared with those of the WKB method to find that WKB approximation works well for the three physically analogical decay modes.     

Decay properties of139mSm and139Eu

The structure of¹³⁹Sm is investigated through the decay properties of^139mSm and¹³⁹Eu. The decay of^139mSm is measured to have a half-life of (10.7±0.6) s. Gamma-ray and internal conversion electron measurements lead to the construction of a decay pattern comprising seven transitions among five states. The decay of¹³⁹Eu with a measured half-life of (17.9± 0.6) s is studied with beta decay spectroscopy techniques. A decay scheme consisting fourteen states in¹³⁹Sm is proposed. Using deducedft values and transition multipolarities,J ^ρ assignments are made. Nuclear systematics of the odd-A, N=77 and 76 are discussed.     

Doubly heavy-quark baryon spectroscopy and semileptonic decay

Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground state of doubly heavy Ξ and Ω baryons. We solve the three-body problem using a variational ansatz made possible by the constraints imposed by heavy-quark spin symmetry. In order to check the dependence of our results on the inter-quark interaction, we have used five different quark-quark potentials which include Coulomb and hyperfine terms coming from one-gluon exchange, plus a confining term. Our results for the spectra are in good agreement with a previous calculation done using a Faddeev approach. For the semileptonic decay our results for the total decay widths are in good agreement with the ones obtained within a relativistic quark model in the quark-diquark approximation.     

Structural and thermodynamic properties of MgB2 from first-principles calculations

A first-principles plane wave method with the relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter (HGH) scheme in the frame of local density approximation is performed to calculate the lattice parameters and the equation of states (EOS) of superconducting MgB₂. Our calculations show that the ratio c/a of about 1.134 is the most stable structure for MgB₂, as is consistent with experiment and other theoretical results. Also, the isothermal and isobaric properties are discussed from energy-volume curves using a quasi-harmonic Debey model.     

Formfactor effects in exclusiveD andB decays

Recent experimental results on the semileptonicD→K ^* transition seem to be in conflict with quark model expectations. Motivated by this finding we reinvestigate the predictions for exclusiveD andB decays in the relativistic quark model approach. Some of the invariant formfactors relevant for the transition matrix elementsD→K ^* andB→D ^* depend strongly on an explicit quarkmass-dependent integral over the meson wave functions. The dependence of decay rates and spectra in semi-leptonicD andB transitions on this integral is analysed and discussed in detail. Furthermore, we discuss how the predictions of the relativistic quark model for semi-leptonicD andB decays can be tested through measurements of the polarization of the produced vector mesonK ^* andD ^*, respectively. Some remarks on exclusive nonleptonic two-body decays of the heavy mesons are also presented. Finally the theoretical uncertainties for the determination of the K-M matrix element |V _ub | from exclusive semi-leptonic decays are discussed.     

Hybrid mesons in the context of the relativistic equation

The flux tube model of hybrid mesons is studied in the context of the relativistic equation in the adiabatic approximation. The moment of inertia of the rigid-rod flux tube is considered in the kinetic part of the interaction. The nonrelativistic and relativistic one scalar bead flux tube is integrated numerically and compared with the adiabatic flux tube small oscillation approximation. The relativistic scalar bead picture suggests that the lowest gluonic excitation of a massive gluon is color octet q q? pair while the conventional mesons are color singlet as usual. We estimate the lowest hybrid charmonium states as 1₁ P = 4.17 ± 0.03 and 1₁D = 4.39±0.05 GeV with color octet qq pair and as 1₁P = 3.78± 0.05 and 1₁D = 4.04±0.09 GeV with color singlet q q? pair. These results are also confirmed by the adiabatic flux tube small oscillation approximation when the hybrid energy gap is adjusted phenomenologically to M _Hc = M _ground + 1GeV.     

Theoretical lifetimes and branching fractions of 2p4(3P)3d 4D7/2, 2F7/2 and 4F7/2 in Ne II

Transition probabilities of the radiative decay processes of the excited levels 2p⁴(³P)3d ⁴D_7/2, ²F_7/2 and ⁴F_7/2 of the fluorine-like neon ion (Ne⁺) are evaluated by variational calculations using superposition of configurations in the Breit-Pauli approximation. The strong ²F_7/2-⁴F_7/2 relativistic mixing is discussed in terms of level designation and doublet-quartet intensity transfer. A detailed comparison of the results with other theories and with the NIST measurements of branching fractions, combined with lifetime measurements, confirms problems on the experimental side.     

The Coulomb sum for electron scattering in the relativistic random phase approximation

The Coulomb sum value for electron scattering is estimated using the relativistic random phase approximation (RPA) in the field theory for nuclear matter. RPA correlations due to σ-, ω- and ϱ-meson exchanges reduce the sum value of the relativistic Hartree approximation by about 15–20%.